Currently, valves for regulating the flow of fluid in refrigeration systems have a structure that comprises                a valve body, provided with an inlet and an outlet for the fluid, which are connected by a connecting compartment,        a connecting compartment flow control device, inserted in an appropriately provided seat formed in the valve body.        
The flow control device comprises a connecting compartment flow control piston, which is functionally connected to an electric motor.
The position of the piston during use is modulated by the action of the electric motor between an open position and a blocking position for the connecting compartment.
During the use of this type of valve, the action of the fluid on the piston is not constant as its position varies with respect to the connecting compartment.
This entails that the flow control device is subjected to different forces depending on the position imparted by the electric motor to the piston.
These forces are substantially due to the difference between the pressures that the fluid applies to a front face of the piston, which is directed toward the connecting compartment, and the pressures that the piston experiences on a rear face thereof that lies opposite thereto.
Pistons are currently known which have connection compartments that cross them, connecting the regions in front of such faces in order to balance the pressures that act thereon in certain operating conditions.
In particular, U.S. Pat. No. 6,568,656 discloses a piston provided with a frustum-shaped head in which there are one or more holes that constitute ports for connection to the described connecting compartments.
A valve according to the teaching of this patent has the frustum-shaped head that is perforated in predefined positions, which are determined in order to minimize the resultant of the pressure forces applied by the fluid to the piston in use when it is in a chosen modulation position with respect to the connecting compartment.
Such predefined positions are determined on the basis of the provided fluid-dynamics behavior of the fluid that during use affects the valve.
Therefore, the holes in the frustum-shaped head are provided at the region where the fluid will have, during use, a pressure which, applied to the rear face of the flow control piston, allows to obtain substantial balancing of the forces that it experiences in the predefined position.
One drawback of a valve provided according to this teaching is that the pressure forces experienced by the piston during use of the valve, despite being substantially balanced when it is in the predefined position, are highly variable with the modulation of its position with respect to the connecting compartment during use of the valve.
Further, a valve provided according to the teaching of this patent is dedicated to a predefined use, its geometry being predetermined as a function of its design operating conditions.
A valve thus dedicated to use in predefined operating conditions therefore does not have a flexibility in application that currently is felt as an increasingly substantial quality, aimed at meeting the standardization requirements that lead to simplicity in logistical management and to lower production cost.